Investigations of cardiac morphology were made in patients with hypertrophic cardiomyopathy (asymmetric septal hypertrophy, ASH) and in patients with congestive cardiomyopathies of various causes. These observations have led to the conclusions that 1) ASH is a disease that involves the architectural arrangement of the muscle cell, particularly that of their contractile elements, and 2) this abnormal arrangement may lead to the generation of abnormal mechanical forces, which in turn may be responsible for the bizarre type of hypertrophy. No distinctive or diagnostic lesion was demonstrated by histologic or ultrastructural study in myocardium of patients with congestive cardiomyopathies.